There are a wide variety of applications for metallic nanostructured particles. For example, high aspect ratio electrically conductive particles can be used in powders or smoke for military ordnance to produce obscuring fogs to scatter radar frequencies. These particles can also be used by themselves, or in paints and coatings for corrosion resistance, reflectivity, modification of electrical properties, or aesthetic purposes.
There are also numerous biotechnology-based applications for metallic nanostructured particles. Gold has been proven to be hypoallergenic and safe to use in a wide variety of biological applications. Spherical gold and silver nanoparticles are currently used as biological stains and/or conjugating agents. Micron size gold colloids are also currently being considered for drug delivery and/or gene delivery.
Current methods for forming metallic nanostructured particles include crystallization and/or mechanical methods, such as grinding. Grinding can be used to convert a roll metal sheet having a nanoscale thickness into platelets. However, grinding is known to produce a significant range of platelet thickness and sizes. Nanoscale layers can also be formed by electroless deposition or by electroplating. However, electroplating systems use toxic chemicals and environmental/disposal costs are high. In addition, plating generally forms films, rather than discrete particles. Non-aqueous techniques incorporating gold salts and a variety of reducing agents have also been disclosed for forming certain metallic nanostructured particles.
In some applications, a substantially monodisperse size distribution of platelets is desirable. High aspect particulate systems are difficult to classify by either size or shape. It is not currently practical to sieve or otherwise separate broad distributions of flake sizes or shapes into narrowing distribution groups particularly for powders with large fractions below mesh 400 (38 microns sieve opening).